Catalyst compositions comprising small silica support materials and methods of use in polymerization reactions

ABSTRACT

Improved catalyst compositions, and polymerization processes using such improved catalyst compositions, are provided. An example of an improved catalyst composition is a supported catalyst system that includes at least one titanium compound, at least one magnesium compound, at least one electron donor compound, at least one activator compound, and at least one silica support material, the at least one silica support material having a median particle size in the range of from 20 to 50 microns with no more than 10% of the particles having a size less than 10 microns and no more than 10% of the particles having a size greater than 50 microns and average pore diameter of at least ≧220 angstroms.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 11/441,505,filed May 26, 2006, now U.S. Pat. No. 7,259,125 which is acontinuation-in-part of Ser. No. 11/151,097, filed Jun. 13, 2005, nowabandoned, herein incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to a polymerization process using improvedcatalyst compositions. Specifically, the catalyst compositions of thepresent invention relate to a Ziegler-Natta type catalyst compound thatincludes a small silica support material, and demonstrate improvedproductivity.

BACKGROUND OF THE INVENTION

Advances in polymerization and catalysis have resulted in the ability toproduce many new polymers having improved physical and chemicalproperties useful in a wide variety of superior products andapplications. With the development of new catalysts, the choice ofpolymerization (solution, slurry, high pressure or gas phase) forproducing a particular polymer have been greatly expanded. Also,advances in polymerization technology have provided more efficient,highly productive and economically enhanced processes.

As with any new technology field, particularly in the polyolefinsindustry, a small savings in cost often determines whether a commercialendeavor is even feasible. The industry has been extremely focused ondeveloping new and improved catalyst systems. Some have focused ondesigning the catalyst systems to produce new polymers, others onimproved operability, and many more on improving catalyst productivity.The productivity of a catalyst, that is, the amount of polymer producedper gram of the catalyst, usually is the key economic factor that canmake or break a new commercial development in the polyolefin industry.

Ziegler-Natta catalyst systems are utilized extensively in commercialprocesses that produce high density and low-density polyethylenes in avariety of molecular weights. Production rates in certain gas phasereactors may be limited in their ability to discharge from the reactorthe polymer particles that are produced during the reaction. In certainof such cases, an increase in the bulk density of the polymer particlesmay increase the production rate of the reactor. Generally,Ziegler-Natta catalysts that have increasing activity and productivity,and that are used in gas phase operations. may tend to produce polymerproducts that have decreasing bulk density. If a reactor is limited inits ability to discharge the polymer product, the use of a high activitycatalyst may result in a decrease in the bulk density of the polymerproduct.

Background references include U.S. Pat. No. 4,405,495 and EP 0 043 220A.

Considering the discussion above, a need exists for higher productivitycatalyst systems capable of providing the efficiencies necessary forimplementing commercial polyolefin processes. Thus, it would be highlyadvantageous to have a polymerization process and catalyst systemcapable of producing polyolefins with improved catalyst productivitiesand reactor performance.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, wherein:

FIG. 1 is an exemplary process flow diagram for an exemplary reactionsystem with which an exemplary catalyst system of the present inventionmay be employed.

FIG. 2 is an exemplary silica dehydration profile used in certainexemplary embodiments of the present invention.

FIG. 3 illustrates particle size distributions for a sample of Davison955 silica, a sample of Davison 955 silica that was screened through 325mesh, and a sample of Ineos ES757 silica.

FIG. 4 is a graphical illustration of ethylene flow versus reaction timefor certain exemplary polymerization processes employing exemplarycatalyst systems that used a variety of exemplary support materials.

FIG. 5 is a graphical illustration of the relationship between catalystsystem productivity and polymer product bulk density for certainexemplary catalyst systems.

FIG. 6 is a graphical illustration of the relationship between catalystsystem productivity and polymer product bulk density for certainexemplary catalyst systems.

While the present invention is susceptible to various modifications andalternative forms, specific exemplary embodiments thereof have beenshown by way of example in the drawings and are herein described indetail. It should be understood, however, that the description herein ofspecific embodiments is not intended to limit the invention to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

It now has been found that polymers (e.g., ethylene homopolymers andcopolymers) readily can be produced with desirable physical propertiesand catalyst system productivities in a low pressure gas phase fluid bedreaction process in the presence of a specific high productivitycatalyst that is impregnated on a porous particulate silica having aparticle size in a particular range, as is also detailed below.

High Activity Catalyst

The compounds used to form the catalysts of the present inventioninclude at least one titanium compound, at least one magnesium compound,at least one electron donor compound, at least one activator compoundand at least one silica material, exemplary embodiments of which areillustrated below.

Generally, the titanium compound has the formulaTi(OR)_(a)X_(b)

wherein

-   -   a. R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical,        or COR′ where R′ is a C₁ to C₁₄ aliphatic or aromatic        hydrocarbon radical;    -   b. X is selected from the group consisting of Cl, Br, I or a        mixture thereof;    -   c. a is 0, 1 or 2;    -   d. b is 1 to 4 inclusive; and    -   e. a+b=3 or 4.

The titanium compounds individually may be present in the catalysts ofthe present invention, or the titanium compounds may be present incombinations thereof. A nonlimiting list of suitable titanium compoundsincludes TiCl₃, TiCl₄, Ti(OCH₃)Cl₃, Ti(OC₆H₅)Cl₃, Ti(OCOCH₃)Cl₃ andTi(OCOC₆H₅)Cl₃.

Generally, the magnesium compound has the formulaMgX₂

wherein

-   -   a. X is selected from the group consisting of Cl, Br, I or        mixtures thereof.

Such magnesium compounds may be present individually in the catalysts ofthe present invention, or the magnesium compounds may be present incombinations thereof. A nonlimiting list of suitable magnesium compoundsincludes MgCl₂, MgBr₂ and MgI₂. In certain exemplary embodiments of thepresent invention, the magnesium compound may be anhydrous MgCl₂.Generally, the magnesium compound may be present in the catalysts of thepresent invention in an amount in the range of from 0.5 to 56 moles ofmagnesium compound per mole of titanium compound. In certain exemplaryembodiments of the present invention, the magnesium compound may bepresent in the catalysts of the present invention in an amount in therange of from 1.5 to 11 moles of magnesium compound per mole of titaniumcompound. In certain exemplary embodiments of the present invention, themagnesium compound may be present in the catalysts of the presentinvention in an amount in the range of from 1.5 to 7 moles of magnesiumcompound per mole of titanium compound. Generally, the titanium compoundand the magnesium compound may be used in a form that will facilitatetheir dissolution in the electron donor compound, as described hereinbelow.

The electron donor compound generally may be any organic compound thatis liquid at 25° C., and that may be capable of dissolving both thetitanium compound and the magnesium compound. A nonlimiting list ofsuitable electron donor compounds includes such compounds as alkylesters of aliphatic and aromatic carboxylic acids, aliphatic ethers,cyclic ethers and aliphatic ketones. In certain embodiments, suitableelectron donor compounds may be alkyl esters of C₁ to C₄ saturatedaliphatic carboxylic acids; alkyl esters of C₇ to C₈ aromatic carboxylicacids; C₂ to C₈, and preferably C₃ to C₄, aliphatic ethers; C₃ to C₄cyclic ethers, and, in certain embodiments, C₄ cyclic mono- ordi-ethers; C₃ to C₆, and, in certain embodiments, C₃ to C₄, aliphaticketones. In certain exemplary embodiments, the electron donor compoundmay be methyl formate, ethyl acetate, butyl acetate, ethyl ether, hexylether, tetrahydrofuran, dioxane, acetone or methyl isobutyl ketone,among others.

The electron donor compounds may be present individually in thecatalysts of the present invention, or they may be present incombinations thereof. Generally, the electron donor compound may bepresent in the range of from 2 to 85 moles of the electron donorcompound per mole of the titanium compound. In certain embodiments, theelectron donor compound may be present in the catalysts of the presentinvention in an amount in the range of from 3 to 10 moles of theelectron donor compound per mole of the titanium compound.

The activator compound generally has the formulaAl(R″)_(c)X′_(d)H_(e)wherein

X′ is Cl, or OR′″;

R″ and R′″ are the same or different, and are C₁ to C₁₄ saturatedhydrocarbon radicals;

d is 0 to 1.5;

e is 1 or 0;

and c+d+e=3.

Such activator compounds may be present individually in the catalysts ofthe present invention, or they may be present in combinations thereof. Anonlimiting list of suitable activator compounds includes Al(C₂H₅)₃,Al(C₂H₅)₂Cl, Al(i-C₄H₉)₃, Al₂(C₂H₅)₃Cl₃, Al(i-C₄H₉)₂H, Al(C₆H₁₃)₃,Al(C₈H₁₇)₃, Al(C₂H₅)₂H and Al(C₂H₅)₂(OC₂H₅).

Generally, the activator compound may be present in the catalysts of thepresent invention in an amount in the range of from 10 to 400 moles ofactivator compound per mole of the titanium compound, and in certainembodiments may be present in the range of from 15 to 60 moles of theactivator compound per mole of the titanium compound, and in certainembodiments may be present in the range of from 2 to 7 moles of theactivator compound per mole of the titanium compound.

The silica support that may be employed in the catalysts of the presentinvention generally has a particle size distribution within the range offrom 2 microns to 100 microns, and a median particle size in the rangeof from 20 microns to 50 microns. In certain exemplary embodiments, thesilica support has a particle size distribution within the range of from2 microns to 80 microns. In certain exemplary embodiments, the silicasupport has a median particle size in the range of from 20 microns to 35microns, and in the range of from 20 to 30 microns in certain exemplaryembodiments. In certain exemplary embodiments, the silica support has aparticle size distribution in which no more than 10% of the particleshave a size below 10 microns, and no more than 10% of the particles havea size greater than 50 microns. In certain exemplary embodiments, thesilica support has a particle size distribution in which no more than10% of the particles have a size below 12 microns, and no more than 8%of the particles have a size greater than 50 microns. As the size of thesilica support decreases, the productivity of the supported catalystgenerally increases, as does the FAR value of film formed from resinproduced by the supported catalyst. In certain exemplary embodiments,this may be accompanied by an increase in the bulk density and adecrease in the average particle size of such resin. Accordingly, thesilica supports used in the improved catalysts of the present inventionmay facilitate, inter alia, greater productivity from the improvedcatalysts as well as the production of polymers having greater bulkdensity. In certain exemplary embodiments, the improved catalysts of thepresent invention comprising these silica supports may have aproductivity (as based on a mass balance) that is at least 3,000 poundspolymer per pound of catalyst per hour; and that is at least 4,500pounds polymer per pound of catalyst per hour in certain exemplaryembodiments, and that is at least 6,000 pounds polymer per pound ofcatalyst per hour in certain exemplary embodiments, and that is at least7,000 pounds polymer per pound of catalyst per hour in certain exemplaryembodiments; and that is at least 9,000 pounds polymer per pound ofcatalyst per hour in certain exemplary embodiments. Certain exemplaryembodiments of the catalysts of the present invention may have evengreater productivities. In certain exemplary embodiments, the polymersproduced from the processes of the present invention that employimproved catalysts that include these silica supports may have a settledbulk density of at least 21.5 pound per cubic foot in certain exemplaryembodiments; and at least 22.5 pound per cubic foot in certain exemplaryembodiments, and at least 23.5 pound per cubic foot in certain exemplaryembodiments; and at least 24.0 pound per cubic foot in certain exemplaryembodiments. Certain exemplary embodiments of the polymers produced fromthe processes of the present invention that employ improved catalyststhat include these silica supports may have even greater settled bulkdensities.

It also may be desirable for such silica support to have a surface areaof ≧200 square meters per gram, and in certain exemplary embodiments,≧250 square meters per gram. In certain exemplary embodiments, theaverage pore volume of such silica support ranges from 1.4 ml/gram to1.8 ml/gram.

The silica support generally should be dry, that is, free of absorbedwater. Drying of the silica support generally is performed by heating itat a temperature of ≧600° C.

In any of the embodiments described herein, the silica or at least onesilica support materials may have an average pore diameter ≧220Angstroms; alternatively, an average pore diameter ≧225 Angstroms;alternatively, an average pore diameter ≧230 Angstroms; alternatively,an average pore diameter ≧235 Angstroms; alternatively, an average porediameter ≧240 Angstroms; alternatively, an average pore diameter ≧245Angstroms; alternatively, an average pore diameter ≧250 Angstroms;alternatively, an average pore diameter ≧255 Angstroms; alternatively,an average pore diameter ≧260 Angstroms; and, alternatively, an averagepore diameter ≧265 Angstroms, as described along with the method ofmeasurement in more detail below.

Catalyst System

Formation of Precursor

The improved catalysts of the present invention may be prepared by firstpreparing a precursor composition from the titanium compound, themagnesium compound, and the electron donor compound, as described below,then impregnating the silica support with the precursor composition, andthen treating the impregnated precursor composition with an activatorcompound as described below.

Generally, the precursor composition may be formed by dissolving thetitanium compound and the magnesium compound in the electron donorcompound at a temperature in the range of from 20° C. up to the boilingpoint of the electron donor compound. The titanium compound can be addedto the electron donor compound before, or after, the addition of themagnesium compound, or concurrent therewith. The dissolution of thetitanium compound and the magnesium compound may be facilitated bystirring, and in some instances by refluxing, these two compounds in theelectron donor compound. After the titanium compound and the magnesiumcompound are dissolved, the precursor composition may be isolated bycrystallization or by precipitation with a C₅ to C₈ aliphatic oraromatic hydrocarbon such as hexane, isopentane or benzene. Thecrystallized or precipitated precursor composition may be isolated,generally in the form of fine, free-flowing particles having an averageparticle size in the range of from 10 to 100 microns.

When prepared according to the procedure above, the precursorcomposition has the formula:Mg_(m)Ti_(l)(OR)_(n)X_(p)[ED]_(q)wherein:

ED is the electron donor compound;

m is ≧0.5 to ≦56, and, in certain exemplary embodiments, ≧1.5 to ≦11;

n is 0, 1 or 2;

p is ≧2 to ≦116, and, in certain exemplary embodiments, ≧6 to ≦14;

q is ≧2 to ≦85, and, in certain exemplary embodiments, ≧3 to ≦10;

R is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical, or COR′wherein R′ is a C₁ to C₁₄ aliphatic or aromatic hydrocarbon radical;

X is selected from the group consisting of Cl, Br, I or mixturesthereof; and

the subscript for the element titanium (Ti) is the arabic numeral one.

Catalyst Preparation: Impregnation of Precursor in Support

The precursor composition then may be impregnated, in a weight ratio ofabout 0.003 to 1, and, in certain exemplary embodiments, about 0.1 to0.33, parts of the precursor composition into one part by weight of thecarrier material.

Before being impregnated, the silica support is dehydrated at 600° C.,and also is treated with an aluminum alkyl compound (e.g., “TEAL”).Dehydrated silica supports that have been treated with TEAL may bereferred to herein as TEAL-on-silica, or “TOS.” The impregnation of thedehydrated, activated silica support (e.g., the TOS) with the precursorcomposition may be accomplished by dissolving the precursor compositionin the electron donor compound, and by then admixing the dehydrated,activated silica support with the precursor composition to impregnatethe dehydrated, activated silica support. The electron donor compoundthen may be removed by drying at temperatures of ≦60° C.

The silica support also may be impregnated with the precursorcomposition by adding the silica support to a solution of the chemicalraw materials used to form the precursor composition in the electrondonor compound, without isolating the precursor composition from suchsolution. The excess electron donor compound then may be removed bydrying, or by washing and drying at temperatures of ≦60° C.

Activation of Precursor Composition

Generally, the precursor composition will be fully or completelyactivated, e.g., it will be treated with sufficient activator compoundto transform the Ti atoms in the precursor composition to an activestate. Suitable activators include, but are not limited to, tri-n-hexylaluminum, triethyl aluminum, diethyl aluminum chloride, trimethylaluminum, dimethyl aluminum chloride, methyl aluminum dichloridetriisobutyl aluminum, tri-n-butyl aluminum, diisobutyl aluminumchloride, isobutyl aluminum dichloride, (C₂H₅)AlCl₂, (C₂H₅O)AlCl₂,(C₆H₅)AlCl₂, (C₆H₅O)AlCl₂, (C₆H₁₂O)AlCl₂ and the corresponding bromineand iodine compounds).

The precursor composition first may be partially activated outside thepolymerization reactor with enough activator compound so as to provide apartially activated precursor composition having an activatorcompound/Ti molar ratio of >0 to <10:1, and, in certain exemplaryembodiments, from 4 to 8:1. This partial activation reaction may becarried out in a hydrocarbon solvent slurry followed by drying of theresulting mixture (to remove the solvent), at temperatures between 20 to80° C., and, in certain exemplary embodiments, between 50 to 70° C. Thesolvent for the activator(s) should be non-polar and capable ofdissolving the activator(s), but not the precursor composition. Amongthe solvents which can be employed to dissolve the activator(s) arehydrocarbon solvents, such as isopentane, hexane, heptane, toluene,xylene, naptha and aliphatic mineral oils such as but not limited toKaydol™, Hydrobrite™ 550 and the like.

The resulting product is a free-flowing solid particulate material thatreadily may be fed to the polymerization reactor. The partiallyactivated and impregnated precursor composition may be fed to thepolymerization reactor where the activation may be completed withadditional activator compound, which may be the same or a differentcompound.

In certain exemplary embodiments, the additional activator compound andthe partially activated impregnated precursor composition optionally maybe fed to the reactor through separate feed lines. In certain of suchembodiments, the additional activator compound may be sprayed into thereactor in either undiluted form (e.g., “neat”), or in the form of asolution of the additional activator compound in a hydrocarbon solvent(e.g., isopentane, hexane, or mineral oil). Such solution may containabout 2 to 30 weight percent of the activator compound. In certain ofsuch embodiments, the additional activator compound may be added to thereactor in such amounts as to provide, along with the amounts ofactivator compound and titanium compound fed with the partiallyactivated and impregnated precursor composition, a total Al/Ti molarratio in the reactor of ≧10 to 400, and, in certain exemplaryembodiments, from 15 to 60. The additional amounts of activator compoundadded to the reactor may react with, and complete the activation of, thetitanium compound in the reactor.

In a continuous gas phase process, such as the fluid bed processdisclosed below, discrete portions of the partially activated precursorcomposition impregnated on the silica support are continuously fed tothe reactor, along with discrete portions of additional activatorcompound, during the continuing polymerization process, and may replaceactive catalyst sites that are expended during the course of thereaction.

In any of the embodiments described herein, the catalyst system mayexhibit high catalyst activity. In certain embodiments, the catalystactivity may be ≧20,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))];alternatively, ≧20,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))];alternatively, ≧21,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))];≧22,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧22,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧25,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧27,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧28,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧28,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧29,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧29,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧30,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; alternatively,≧32,500 (g polymer), e.g., polyethylene/[(mmol Ti)(h))]; and,alternatively, ≧35,000 (g polymer), e.g., polyethylene/[(mmol Ti)(h))].

In other embodiments, alternatively stated, the catalyst activity may be≧6,500 (g polymer), e.g., polyethylene/(g precursor); alternatively,≧7,000 (g polymer), e.g., polyethylene/(g precursor); alternatively,≧7,250 (g polymer), e.g., polyethylene/(g precursor); alternatively,≧7,500 (g polymer), e.g., polyethylene/(g precursor); alternatively,≧8,000 (g polymer), e.g., polyethylene/(g precursor); alternatively,≧8,500 (g polymer), e.g., polyethylene/(g precursor); and alternatively,≧9,000 (g polymer), e.g., polyethylene/(g precursor).

Polymerization

The polymerization may be conducted by contacting a stream ofmonomer(s), in a gas phase process (such as in the fluid bed processdescribed below), and substantially in the absence of catalyst poisons(e.g., moisture, oxygen, CO, CO₂, and acetylene) with a catalyticallyeffective amount of the completely activated precursor composition at atemperature and at a pressure sufficient to initiate the polymerizationreaction.

In order to achieve the desired density ranges in certain exemplarycopolymers produced by the present invention, it may be well tocopolymerize enough of the ≧C₃ comonomers with ethylene to achieve alevel of >0 to 10 mol percent of the C₃ to C₈ comonomer in thecopolymer. The amount of comonomer that may be used to achieve thisresult will depend on the particular comonomer(s) employed.

Table 1 below provides a listing of the amounts, in moles, of variouscomonomers that may be copolymerized with ethylene in order to providepolymers having a desired density range (e.g., within the range of from0.91 to 0.97) at any given melt index. Table 1 also indicates therelative molar concentration, of such comonomers to ethylene, which maybe present in the recycled gas stream of monomers under reactionequilibrium conditions in the reactor.

TABLE 1 Gas Stream Comonomer/Ethylene Comonomer Mole % in copolymermolar ratio propylene >0 to 10 >0 to 0.9 butene-1 >0 to 7.0 >0 to 0.7pentene-1 >0 to 6.0 >0 to 0.45 hexene-1 >0 to 5.0 >0 to 0.4 octene-1 >0to 4.5 >0 to 0.35

Referring now to FIG. 1, illustrated therein is an exemplary fluidizedbed reaction system that may be used in the practice of the processes ofthe present invention. With reference thereto, the reactor 1 generallyincludes a reaction zone 2 and a velocity-reduction zone 3.

The reaction zone 2 includes a bed of growing polymer particles, formedpolymer particles and a minor amount of catalyst particles fluidized bythe continuous flow of gaseous components in the form of make-up feedand recycle gas through the reaction zone 2. To maintain a viablefluidized bed, the mass gas flow rate through the bed generally will beabove the minimum flow required for fluidization, and, in certainexemplary embodiments, may be in the range of from 1.5 to 10 timesG_(mf) and, in certain exemplary embodiments, in the range of from 3 to6 times G_(mf). G_(mf) is used in the accepted form as the abbreviationfor the minimum mass gas flow required to achieve fluidization, as maybe set forth further in, for example, C. Y. Wen and Y. H. Yu, “Mechanicsof Fluidization,” Chemical Engineering Progress Symposium Series, Vol.62, p. 100-111 (1966).

Generally, the bed will contain particles that may prevent the formationof localized “hot spots” and that may entrap and distribute theparticulate catalyst throughout the reaction zone 2. On start up, thereactor 1 usually may be charged with a base of particulate polymerparticles before gas flow is initiated. Such particles may be identicalin nature to the polymer to be formed, or may be different therefrom.When different, the particulate polymer particles provided as a base maybe withdrawn with the desired formed polymer particles as the firstproduct. Eventually, a fluidized bed of the desired polymer particlessupplants the start-up bed.

In certain exemplary embodiments, the partially activated precursorcomposition (impregnated on the SiO₂ support) used in the fluidized bedmay be stored for service in a reservoir 4 under a blanket of a gas thatis inert to the stored material, such as nitrogen or argon.

Fluidization is achieved by a high rate of gas recycle to and throughthe bed, typically in the order of about 50 times the rate of feed ofmake-up gas. The fluidized bed has the general appearance of a densemass of viable particles in possible free-vortex flow as created by thepercolation of gas through the bed. The pressure drop through the bedmay be equal to, or slightly greater than, the mass of the bed dividedby the cross-sectional area, and thus may depend on the geometry of thereactor 1.

Make-up gas may be fed to the bed at a rate equal to the rate at whichparticulate polymer product is withdrawn. The composition of the make-upgas may be determined by a gas analyzer 5 positioned above the bed. Thegas analyzer 5 may determine the composition of the gas being recycled,and the composition of the make-up gas may be adjusted accordingly tomaintain an essentially steady state gaseous composition within thereaction zone 2.

To facilitate complete fluidization, the recycle gas and, where desired,part of the make-up gas, may be returned over gas recycle line 6 to thereactor 1 at point 7 below the bed. A gas distribution plate 8 may belocated at this point above the point of return to aid in fluidizing thebed.

The portion of the gas stream that does not react in the bed constitutesthe recycle gas which is removed from the reaction zone 2, preferably bypassing it into a velocity reduction zone 3 above the bed whereentrained particles may be given an opportunity to drop back into thebed.

The recycle gas then may be compressed in a compressor 9 and then passedthrough a heat exchanger 10 wherein the heat of reaction may be removedfrom it before it is returned to the bed. The temperature of the bed iscontrolled at an essentially constant temperature under steady stateconditions by constantly removing heat of reaction. No noticeabletemperature gradient exists within the upper portion of the bed. Atemperature gradient will exist in the bottom of the bed in a layer ofabout 6 to 12 inches, between the temperature of the inlet gas and thetemperature of the remainder of the bed. The recycle gas is thenreturned to the reactor 1 at its base 7 and to the fluidized bed throughdistribution plate 8. The compressor 9 also can be placed downstream ofthe heat exchanger 10.

The distribution plate 8 may play an important role in the operation ofthe reactor 1. The fluidized bed contains growing and formed particulatepolymer particles as well as catalyst particles. As the polymerparticles are hot and possibly active, it may be well to prevent themfrom settling, for if a quiescent mass is allowed to exist, any activecatalyst contained therein may continue to react and cause fusion.Diffusing recycle gas through the bed at a rate sufficient to maintainfluidization throughout the bed is, therefore, beneficial. Thedistribution plate 8 serves this purpose, and may be a screen, slottedplate, perforated plate, a plate of the bubble cap type and the like.The elements of the distribution plate 8 all may be stationary, or thedistribution plate 8 may be of the mobile type disclosed in U.S. Pat.No. 3,298,792. Whatever its design, it generally will diffuse therecycle gas through the particles at the base of the bed to keep the bedin a fluidized condition, and also serve to support a quiescent bed ofresin particles when the reactor 1 is not in operation. The mobileelements of the distribution plate 8 may be used to dislodge any polymerparticles entrapped in or on the distribution plate 8.

Hydrogen may be used as a chain transfer agent in the polymerizationreaction of the present invention. The ratio of hydrogen/ethylenemonomer employed generally will vary between 0 to 2.0 moles of hydrogenper mole of the ethylene monomer in the gas stream.

Any gas inert to the catalyst and reactants can also be present in thegas stream. In certain exemplary embodiments, the activator compound maybe added to the reaction system downstream from heat exchanger 10. Thus,the activator compound may be fed into the gas recycle system fromdispenser 11 through line 12.

Compounds of the formula Zn(R_(a))(R_(b)), wherein R_(a) and R_(b) arethe same or different C₁ to C₁₄ aliphatic or aromatic hydrocarbonradicals, may be used (in conjunction with hydrogen), with the catalystsof the present invention, as molecular weight control or chain transferagents, e.g., to increase the melt index values of the copolymers thatare produced. From 0 to 100, and, in certain embodiments, from 20 to 30moles of the Zn compound (as Zn) would be used in the gas stream in thereactor 1 per mol of titanium compound (as Ti) in the reactor 1. Thezinc compound would be introduced into the reactor 1, preferably in theform of a dilute solution (2 to 30 weight percent) in a hydrocarbonsolvent or absorbed on a solid diluent material, such as silica, inamounts of 10 to 50 weight percent. These compositions tend to bepyrophoric. The zinc compound may be added alone, or with any additionalportions of the activator compound that are to be added to the reactor1, from a feeder (not shown) which could be positioned adjacentdispenser 11.

Generally, the fluid bed reactor 1 will be operated at a temperaturebelow the sintering temperature of the polymer particles to ensure thatsintering will not occur. For the production of the polymers in theprocess of the present invention, an operating temperature of 30 to 150°C. generally may be employed. In certain exemplary embodiments,temperatures of 70 to 95° C. may be used to prepare products having adensity in the range of from 0.91 to 0.92, and temperatures in the rangeof from 80 to 100° C. may be used to prepare products having a densityin the range of >0.92 to 0.94.

The fluid bed reactor 1 is operated at pressures of up to 1000 psi, andin certain exemplary embodiments may be operated at a pressure of from150 to 400 psi, with operation at the higher pressures in such rangesfavoring heat transfer, because, inter alia, an increase in pressureincreases the unit volume heat capacity of the gas.

The partially activated and SiO₂ supported precursor composition isinjected into the bed at a rate equal to its consumption at a point 13that is above the distribution plate 8. In certain exemplaryembodiments, the catalyst may be injected at a point in the bed wheregood mixing of polymer particles occurs. The injection of the catalystat a point above the distribution plate 8 may be beneficial because,inter alia, the catalysts used in the practice of the invention arehighly active, such that injection of the catalyst into the area belowthe distribution plate 8 may cause polymerization to begin there andeventually cause plugging of the distribution plate 8. Injection intothe viable bed, instead, aids in distributing the catalyst throughoutthe bed and tends to preclude the formation of localized spots of highcatalyst concentration which may result in the formation of “hot spots.”Injection of the catalyst into the reactor 1 above the bed may result inexcessive catalyst carryover into the recycle line where polymerizationmay begin and plugging of the line and heat exchanger 10 eventually mayoccur.

A gas that is inert to the catalyst, such as nitrogen or argon, may beused to carry the partially reduced precursor composition, and anyadditional activator compound or non-gaseous chain transfer agent thatis used, into the bed.

The production rate of the bed is controlled by the rate of catalystinjection. The production rate may be increased by simply increasing therate of catalyst injection, and may be decreased by reducing the rate ofcatalyst injection.

Because any change in the rate of catalyst injection will change therate of generation of the heat of reaction, the temperature of therecycle gas entering the reactor 1 may be adjusted upwards and downwardsto accommodate the change in rate of heat generation. This facilitatesthe maintenance of an essentially constant temperature in the bed.Complete instrumentation of both the fluidized bed and the recycle gascooling system may be useful to facilitate, inter alia, the detection ofany temperature change in the bed so as to enable the operator to make asuitable adjustment in the temperature of the recycle gas.

Under a given set of operating conditions, the fluidized bed ismaintained at essentially a constant height by withdrawing a portion ofthe bed as product at a rate equal to the rate of formation of theparticulate polymer product. Because the rate of heat generation isdirectly related to product formation, a measurement of the temperaturerise of the gas across the reactor 1 (the difference between inlet gastemperature and exit gas temperature) may be determinative of the rateof particulate polymer formation at a constant gas velocity.

In certain exemplary embodiments, the particulate polymer product may becontinuously withdrawn at a point 14 at or close to the distributionplate 8 and in suspension with a portion of the gas stream that may bevented as the particles settle to minimize further polymerization andsintering when the particles reach their ultimate collection zone. Thesuspending gas may also be used to drive the product of one reactor toanother reactor.

The particulate polymer product conveniently may be withdrawn throughthe sequential operation of a pair of timed valves 15 and 16 defining asegregation zone 17. While valve 16 is closed, valve 15 may be opened toemit a plug of gas and product to the zone 17 between it and valve 15,which then may be closed. Valve 16 then may be opened to deliver theproduct to an external recovery zone. Valve 16 then may be closed toawait the next product recovery operation. The vented gas containingunreacted monomers may be recovered from zone 17 through line 18 andrecompressed in compressor 19 and returned directly, or through apurifier 20, over line 21 to gas recycle line 6 at a point upstream ofthe recycle compressor 9.

Finally, the fluidized bed reactor 1 is equipped with an adequateventing system to allow venting of the bed during start up and shutdown. The reactor 1 does not require the use of stirring means and/orwall scraping means. The recycle gas line 6 and the elements therein(e.g., compressor 9, heat exchanger 10) generally should have smoothsurfaces, and should be devoid of unnecessary obstructions so as not toimpede the flow of recycle gas.

The highly active catalyst system of this invention may yield a fluidbed product having an average particle size of from 0.01 to 0.04 inches,and, in certain exemplary embodiments, from 0.02 to 0.03 inches, indiameter wherein the catalyst residue may be very low. The polymerparticles are relatively easy to fluidize in a fluid bed.

The feed stream of gaseous monomer, with or without inert gaseousdiluents, may be fed into the reactor at a space time yield of about 2to 10 pounds/hour/cubic foot of bed volume.

The term virgin resin or polymer as used herein means polymer, ingranular form, as it is recovered from the polymerization reactor.

The catalysts of the present invention also may be used in the gas phasereaction process and apparatus disclosed in U.S. Pat. No. 4,255,542,which corresponds to European Patent Application No. 79101169.5, whichwas filed Apr. 17, 1979 and which was published on Oct. 31, 1979 asPublication No. 4966. These references disclose the use of an entirelystraight sided fluid bed reactor that employs heat exchange means withinthe reactor.

Polymer(s)

A variety of polymers may be produced as products of the methods of thepresent invention. The polymers that may be prepared with the catalystsof the present invention include, inter alia, copolymers that include amajor mol percent (e.g., ≧90%) of ethylene, and a minor mol percent(e.g., ≦10%) of one or more C₃ to C₈ alpha olefins. Generally, the C₃ toC₈ alpha olefins will not contain any branching on any of their carbonatoms that may be closer than the fourth carbon atom from the doublebond. Examples of suitable C₃ to C₈ alpha olefins include, but are notlimited to, propylene, butene-1, pentene-1, hexene-1,4-methyl pentene-1,heptene-1 and octene-1. In certain exemplary embodiments of the presentinvention, the C₃ to C₈ alpha olefins may include propylene, butene-1,hexene-1,4-methyl pentene-1 and octene-1.

The polymers that may be prepared with the catalysts of the presentinvention generally have a molecular weight distribution (Mw/Mn) in therange of from 2.5 to 6.0. In certain exemplary embodiments of thepresent invention, the polymers may have a molecular weight distributionin the range of from 2.7 to 4.1. Another means of indicating themolecular weight distribution value (Mw/Mn) of a polymer involves aparameter referred to as the melt flow ratio (MFR). For the polymers ofthe present invention, an MFR range of ≧20 to ≦40 corresponds to a Mw/Mnvalue range of 2.5 to 6.0, and an MFR value range of ≧22 to ≦32corresponds to an Mw/Mn value range of 2.7 to 4.1.

The polymers that may be prepared with the catalysts of the presentinvention generally have a density in the range of from ≧0.91 to ≦0.97.In certain exemplary embodiments, the polymers may have a density in therange of from ≧0.916 to ≦0.935. In certain exemplary embodiments, thedensity of certain exemplary copolymers that may be prepared with thecatalysts of the present invention, at a given copolymer melt indexlevel, may be regulated by, inter alia, the amount of the one or more C₃to C₈ comonomers that may be copolymerized with the ethylene. In certainembodiments of the present invention in which C₃ to C₈ comonomers arenot reacted with ethylene in the presence of a catalyst of the presentinvention, the ethylene generally will homopolymerize with the catalystsof the present invention, thereby providing homopolymers. In certainexemplary embodiments, the homopolymers produced in accordance with thepresent invention may have a density of ≧0.96. Thus, the density of thepolymers that may be prepared with the catalysts of the presentinvention progressively may be lowered through the addition ofprogressively larger amounts of one or more C₃ to C₈ comonomers. Theamount of each of the various C₃ to C₈ comonomers that may be used toprovide a copolymer having a desired density generally will vary fromcomonomer to comonomer, under the same reaction conditions. Thus, for anoperator to provide a copolymer having the same given density at a givenmelt index level, the operator generally may add larger molar amounts ofthe different C₃ to C₈ comonomers, in the following order:C₃>C₄>C₅>C₆>C₇>C₈.

The polymers that may be prepared with the catalysts of the presentinvention generally have a standard or normal load melt index in therange of from ≧0.01 to about 100. In certain exemplary embodiments, thepolymers may have a standard or normal load melt index in the range offrom 0.5 to 80. The polymers may have a high load melt index (HLMI) inthe range of from 11 to 2000. The melt index of the polymers that may beprepared with the catalysts of the present invention may be a functionof a variety of factors including, inter alia, the temperature of thepolymerization reaction, the density of the copolymer, the ratio ofhydrogen to ethylene monomer present during the reaction, and the ratioof C₃ to C₈ comonomer to ethylene monomer present during the reaction.Thus, an operator may increase the melt index of the polymers by, interalia, increasing the polymerization temperature, and/or by decreasingthe density of the copolymer, and/or by increasing the hydrogen/ethylenemonomer ratio, and/or by increasing the ratio of C₃ to C₈ comonomer toethylene monomer. In addition to hydrogen, an operator optionally mayinclude other chain transfer agents (e.g., dialkyl zinc compounds) tofurther increase the melt index of the polymers.

The polymers of the present invention generally have an unsaturatedgroup content of ≦1. In certain exemplary embodiments, the polymers ofthe present invention may have an unsaturated group content in the rangeof from ≧0.1 to ≦0.3 carbon-carbon double bond per 1000 carbon atoms.

The polymers of the present invention generally have a residual catalystcontent, which may vary depending on the productivity of the catalystsystem. For a catalyst system having a productivity level of ≧100,000pounds of polymer per pound of residual metal in the polymer, thepolymers of the present invention produced through a process using suchcatalyst system may have a residual catalyst content, expressed in termsof parts per million (ppm) of titanium metal, in the range of from >0 to≦10 ppm. For catalyst systems having a productivity level of ≧200,000pounds of polymer per pound of residual metal in the polymer, theresidual catalyst content may be in the range of from >0 to ≦5 ppm. Forcatalyst systems having a productivity level of ≧500,000 pounds ofpolymer per pound of residual metal in the polymer, the residualcatalyst content in the polymers produced therefrom may be in the rangeof from >0 to ≦2 ppm. The homopolymers and copolymers of the presentinvention are readily produced by the processes of the present inventionat productivities of up to 500,000 pounds of polymer per pound ofresidual metal in the polymer.

The polymers of the present invention generally are granular materialsthat have an average particle size in the range of from 0.01 to 0.06inches in diameter. In certain embodiments, the polymers have an averageparticle size in the range of from 0.02 to 0.03 inches, in diameter. Theparticle size may be an important factor for the purposes of readilyfluidizing the polymer particles in a fluid bed reactor. The granularcopolymers and homopolymers of the present invention have a bulk densityin the range of from 19 pounds per cubic foot to 35 pounds per cubicfoot. Expressed in different units, the granular copolymers andhomopolymers of the present invention have a bulk density in the rangeof from 0.304 gram per cubic centimeter to 0.561 gram per cubiccentimeter.

The polymers of the present invention may be useful in a variety ofmanners, including, but not limited to, the production of filmtherefrom, as well as in other molding applications. When the polymersof the present invention are to be used for film-making purposes, anoperator may elect to use embodiments of the polymers of the presentinvention that have a density in the range of from ≧0.916 to ≦0.935, andin certain embodiments, a density in the range of from ≧0.917 to ≦0.928;a molecular weight distribution (Mw/Mn) in the range of from ≧2.7 to≦4.1, and in certain embodiments, a molecular weight distribution(Mw/Mn) in the range of from ≧2.8 to ≦3.1; and a standard melt index inthe range of from >0.5 to ≦5.0, and in certain embodiments, a standardmelt index in the range of from ≧0.7 to ≦4.0. Generally, the films thatmay be produced from the polymers of the present invention may have athickness in the range of from >0 to ≦10 mils, and in certainembodiments, a thickness in the range of from >0 to ≦5 mils, and incertain embodiments, a thickness in the range of from >0 to ≦1 mil.

When the polymers of the present invention are to be used in injectionmolding of flexible articles (e.g., houseware materials), an operatormay elect to use embodiments of the polymers of the present inventionthat have a density in the range of from ≧0.920 to ≦0.940, and incertain exemplary embodiments, a density in the range of from ≧0.925 to≦0.930; a molecular weight distribution Mw/Mn in the range of from ≧2.7to ≦3.6, and in certain embodiments a molecular weight distributionMw/Mn in the range of from ≧2.8 to ≦3.1; and a standard melt index inthe range of from ≧2 to ≦100, and in certain embodiments a standard meltindex in the range of from ≧8 to ≦80.

To facilitate a better understanding of the present invention, thefollowing examples of some of the exemplary embodiments are given. In noway should such examples be read to limit, or to define, the scope ofthe invention.

EXAMPLE 1

For laboratory-prepared precursors, silicas first were dehydrated undernitrogen flow in a laboratory Carbolite Vertical Furnace, Model No. VST12/32/400/2408 CP-FM supplied by Carbolite, Inc., provided with a quartzglass tube of 3.0 cm outer diameter and 70 cm in total length, and twothermocouples. One thermocouple was placed in a thermowell within thequartz glass tube, while the other was affixed to the skin of the quartzglass tube by placing it between the two folding halves of the furnace,then clamping the folding halves shut. The thermocouples were hooked upto a Nomad OM-SP1700 data logger supplied by Omega Engineering. Acollection flask for excess blowout silica was attached at the top ofthe tube, which in turn was attached to a bubbler via a glass elbow.

About 25-30 grams of silica was poured via a funnel into the quartzglass tube to fill the tube about ⅔ full within the heating zone. Apreset program was started to begin the dehydration, using a Eurotherm2408 Programmable Temperature Controller. A typical ramp and soakprofile is shown in FIG. 2. The gas flow (in this case nitrogen) waspreset to about 50-100 cubic centimeters per minute.

At the end of the dehydration cycle (typically overnight), the silicawas discharged into a clean, dry, N₂-purged bottle and maintained in aninert atmosphere. The data logger information was downloaded to acomputer file.

Three different silicas, (DAVISON-955™ silica (comparative), screenedDAVISON-955™ silica (comparative), and INEOS ES757™ silica (inventive),were used to prepare laboratory-scale supported catalyst precursorcompositions. Certain properties of these silicas are presented in theTables 2 and 3 below. The screened Davison-955 silica consisted of thefraction of Davison 955 silica that passed through a 325 mesh (44 μm)screen.

TABLE 2 Summary of B.E.T. Surface Area and Pore Volume of Davison 600,Davison 955 Screened (through 325 Mesh) and Ineos ES757 Silicas SingleCumulative 5-pt B.E.T. Cumulative Cumulative Point Total AdsorptionSurface Adsorption Desorption Pore Volume Pore Volume Silica Type Aream²/g S.A. m²/g S.A m²/g cc/g cc/g Davison 955 317.5453 330.0554 407.91661.646722 1.618345 Davison 955 - 306.1673 306.3902 376.0159 1.6529321.619226 Dehydrated at 600° C. Davison 955 - 330.6516 336.0729 398.60511.643374 1.607446 Screened (through 325 Mesh) Ineos ES757 280.1078270.5909 339.8820 1.601038 1.568156 Ineos ES757 - 269.6506 264.4110331.4600 1.567730 1.536919 Dehydrated at 600° C.

TABLE 3 Summary of Pore Size by B.E.T. of Davison 600, Davison 955Screened (through 325 Mesh) and Ineos ES757 Silicas Cumulative AveragePore Adsorption Desorption Desorption Diameter Average Pore Average PorePore Volume Angstroms Diameter Diameter Silica Type cc/g (4 V/A byB.E.T.) (4 V/A) (4 V/A) Davison 955 1.635965 207.0535 196.1302 160.4215Davison 955 - 1.637997 215.9515 211.394 174.2476 Dehydrated at 600° C.Davison 955 - 1.625029 198.8043 191.3211 163.0715 Screened (through 325Mesh) Ineos ES757 1.587304 228.6317 231.8121 186.8064 Ineos ES757 -1.555146 232.5572 232.5045 187.6722 Dehydrated at 600° C.

The nitrogen adsorption/desorption analysis was performed on aMicromeritics Accelerated Surface Area & Porosimetry instrument (ASAP2405). The silica samples were out-gassed overnight at 200° C. whileunder vacuum prior to analysis to remove any physisorbed species (i.e.,moisture) from the sample's surface. Approximately 0.5 gram of samplewas used for the analysis.

Typically, B.E.T. surface areas, corresponding to the methodologydeveloped by Brunauer, Emmett, and Teller, are achieved with a precisionof <3% relative standard deviation (RSD). The instrument employs astatic (volumetric) method of dosing samples and measures the quantityof gas (nitrogen) that can be physically adsorbed (physisorbed) on asolid at liquid nitrogen temperature. For the multi-point B.E.T.measurement, the volume of nitrogen uptake was measured at 5pre-selected relative pressure points (0.06, 0.08, 0.12, 0.16, and 0.20)at constant temperature. The relative pressure is the ratio of theapplied nitrogen pressure to the vapor pressure of nitrogen at theanalysis temperature of 77 K. Pore sizes >˜3,000 Å diameter (>0.30 μm)are not detected by this method but can be detected with mercuryporosimetry.

Test conditions for the nitrogen adsorption/desorption isotherms include15 second equilibration interval, 97-point pressure table (40 adsorptionpoints, 40 desorption points, 5-point B.E.T. surface area, 15 microporepoints, and 1-point total pore volume), 2.5%/2.5 mmHg P/Po tolerance,and 120 min Po interval.

The B.E.T. surface area, pore volume, and pore size results includesurface area and porosimetry data for pore sizes up to ˜3,000 angstromsdiameter for the silica samples. The adsorption and desorption resultsincludes pore sizes between ˜17-3,000 Å diameter, ˜0.0017-0.3 μm. Asingle point TPV was input at P/Po 0.995.

There was complete closure of desorption curve with the adsorption curvefor the silica samples. However, differences in results in adsorptionvs. desorption data can occur and is largely because desorption processbehaves differently than the adsorption process. Typically, an adsorbategas (nitrogen) will desorb much slower than when it condenses to fill amaterial's pores.

Generally, desorption branch of an isotherm is used to relate the amountof adsorbate lost in a desorption step to the average size of poresemptied in the step. A pore loses its condensed liquid adsorbate, knownas the core of the pore, at a particular relative pressure related tothe core radius by the Kelvin equation. After the core is evaporated, alayer of adsorbate remains on the wall of the pore. The thickness ofthis adsorbed layer is calculated for a particular relative pressurefrom the thickness equation. This layer becomes thinner with successivedecreases in pressure, so that the measured quantity of gas desorbed ina step is composed of a quantity equivalent to the liquid coresevaporated in that step plus the quantity desorbed from the pore wallsof pores whose cores have evaporated in that and previous steps.Barrett, Joyner, and Halenda [Barrett, E. P., Joyner, L. G., Halenda, P.P., J. Am. Chem. Soc. 1951 73 373-380.] developed the method (known asthe BJH method) which incorporates these ideas.

A pore filled with condensed liquid nitrogen has 3 zones:

The core—evaporates all at once when the critical pressure for thatradius is reached; the relationship between the core radius and thecritical pressure is defined by the Kelvin equation. The adsorbedlayer—composed of adsorbed gas that is stripped off a bit at a time witheach pressure step; the relationship between the thickness of the layerand the relative pressure is defined by the thickness equation. Thewalls of the cylindrical pore itself—the diameter of the empty pore isrequired to determine the pore volume and area. End area is neglected.

The recommendation for using either adsorption or desorption data is touse the adsorption data instead of the desorption data for comparingresults between samples. Typically, the adsorption process is very cleanfor BJH calculations. The desorption process of N₂ out of bottle-shapedpores can not usually distinguish what fraction of pores is open vs.closed (some open-ended vs. some closed-ended pores).

In general, the BET surface area, single point total pore volume (TPV),and average pore diameter (4V/A by BET) is best to use for comparingsample data since it also would include any micropore data <˜17 Ådiameter but not <˜4-5 Å diameter. However, the adsorption data can alsobe used for comparing sample data but is limited to surface area andporosimetry analysis between ˜17 and ˜3,000 Å diameter.

The hydroxyl content of the three silicas dehydrated at 600° C. wascharacterized by titration with TiCl₄ in a hexane solution. Afterwashing and drying of the treated silica, the titanium content of thetreated silica (a measure of the presence of hydroxyl groups in thesilica) was determined by a spectrophotometric method. The hydroxylcontent of the three silicas is reported in the table below. Thehydroxyl content was determined by TiCl₄ titration that binds to thesurface OH-groups. The final titanium content, measured by aspectrophotometric method, is an indication of the OH-group content at agiven dehydration temperature of the silica.

TABLE 4 Hydroxyl Content at 600° C. as determined by TiCl₄ titrationSilica Type (mmol OH/g) Davison 955 0.59 Screened Davison-955 0.55 IneosES757 0.59

The silicas used as support material in the three laboratory-scalecatalyst precursors have a particle size distribution, measured in aMALVERN Mastersizer 2000 analyzer, as shown below, and in FIG. 3.

TABLE 5 MALVERN Particle Size Distribution of Davison 600, Davison 955Screened (through 325 Mesh) and Ineos ES757 Silicas Size Davison 955Davison 955 Ineos ES757 μm Volume % Screened Volume % 0.02 0 0 0 0.025 00 0 0.028 0 0 0 0.032 0 0 0 0.036 0 0 0 0.04 0 0 0 0.045 0 0 0 0.05 0 00 0.056 0 0 0 0.063 0 0 0 0.071 0 0 0 0.08 0 0 0 0.089 0 0 0 0.1 0 0 00.112 0 0 0 0.126 0 0 0 0.142 0 0 0 0.159 0 0 0 0.178 0 0 0 0.2 0 0 00.224 0 0 0 0.283 0 0 0 0.317 0 0 0 0.356 0 0 0 0.399 0.448 0 0 0 0.5020 0 0 0.564 0 0 0 0.632 0 0 0 0.71 0 0 0 0.796 0 0 0 0.893 0 0 0 1.002 00 0 Davison 955 Size Davison 955 Screened Ineos ES757 μm Volume % Volume% Volume % 1.125 0 0 0 0.262 0 0 0 1.416 0 0 0 1.589 0 0 0 1.783 0 0 0 20 0 0 2.24 0 0 0 2.518 0 0 0 2.825 0 0 0 3.17 0 0 0 3.557 0 0 0 3.991 00 0 4.477 0.02 0 0 5.024 0.07 0 0 5.637 0.26 0 0 6.325 0.48 0 0 7.0960.76 0.02 0 7.962 1.12 0.09 0.03 8.934 1.53 0.39 0.14 10.024 2.01 0.930.53 11.247 2.53 1.81 1.25 12.619 3.08 3.06 2.35 14.159 3.65 4.66 3.915.887 4.2 6.47 5.79 17.825 4.71 8.34 7.86 20.000 5.15 9.92 9.76 22.4405.53 11.01 11.23 25.179 5.58 11.36 11.92 28.251 5.98 10.87 11.67 31.6986.06 9.36 10.51 35.566 6.04 7.86 8.66 39.905 5.92 5.83 6.45 44.77444.774 5.7 3.92 4.3 50.238 5.39 2.35 2.45 56.368 4.99 1.16 1.04 63.2464.5 0.31 0.16 70.963 3.94 0 0 79.621 3.31 0 0 89.337 2.66 0 0 100.2372.02 0 0 112.468 1.41 0 0 126.191 0.9 0 0 141.589 0.27 0 0 158.866 0.010 0 178.250 0 0 0 200.000 0 0 0 224.404 0 0 0 251.785 0 0 0 282.508 0 00 316.979 0 0 0 355.656 0 0 0 399.052 0 0 0 447.744 0 0 0 502.377 0 0 0563.677 0 0 0 632.456 0 0 0 709.627 0 0 0 796.214 0 0 0 893.367 0 0 01002.374 0 0 0 1124.683 0 0 0 1261.915 0 0 0 1415.892 0 0 0 1588.656 0 00 2000.000

The particle size distribution was measured with accuracy ±1% on theD(0.5) in the size range 0.020-2000.000 microns. Measurements were madein n-heptane dispersion at room temperature using Hydro 2000S, smallvolume general-purpose automated sample dispersion unit.

Values of silicas particle size distribution are given in Table 6, whereD(0.5) refers to the particle size in micron at which 50 w % of thesample is below that value, D(0.1) and D(0.9) respectively, 10 and 90 w% of the sample below. Span is a measure of particle sizedistribution=[D(0.9)−D(0.1)]/D(0.5).

TABLE 6 Particle Size Distribution of Davison 955, Screened (through 325Mesh), and Ineos ES757 Silicas Determined by MALVERN Analysis D (0.1) D(0.5) D (0.9) Silica Type μm μm μm Span Davison 955 13.244 33.638 81.1392.02 Davison 955 - Screened 15.562 26.033 42.617 1.04 (through 325 Mesh)Ineos ES757 16.541 26.989 42.966 0.98

As shown in Tables 2, 3 and 5, Davison-955 silica has higher surfacearea and comparable pore volume than Ineos ES757 silica. However, IneosES757 silica has larger average pore diameter and smaller averageparticle size and narrower particle size distribution than Davison 955silica.

About 9.5 grams of each of the three types of silica was placed in anoven-dried, air-free 100 mL Schlenk flask having a stir bar and rubberseptum, to which about 50 ml of dry, degassed hexane and 3 mL oftriethylaluminum (TEAL) heptane solution (1.54 M) were added. Each ofthe three mixtures was stirred for about 30 minutes in an oil bath at40° C., after which point the oil bath temperature was raised to 70° C.and vacuum dried to complete dryness. The resulting mixtures may bereferred to as laboratory TEAL-on-silica (laboratory TOS).

For each type silica, laboratory catalyst precursor compositions at moleratios Mg/Ti=3 and Mg/Ti=5 were prepared according to the followingprocedure. In an oven dried, air-free 100 mL Schlenk flask provided withstir bar and rubber septum, about 0.35 grams of [TiCl₃, 0.33 AlCl₃], and0.50 g of MgCl₂ were mixed in 18.5 mL of dry, degassed tetrahydrofuran(THF) supplied by Aldrich. The compound referred to as [TiCl₃, 0.33AlCl₃] is a mixed compound that is obtained by reduction of TiCl₃ withmetallic aluminum; the mixed compound thus contains 1 molecule of AlCl₃per 3 molecules of TiCl₃. The operation was carried out in a “dry box.”The flask was then placed in an oil bath over a stir/heating plateinside a hood. The septum was replaced by a condenser with a glass jointand provided with circulating cold water and a small N₂ flow through it.The oil bath was heated at 80° C., resulting in an internal temperaturebetween 70 and 72° C. The system was maintained under stirring for about2 hours until all solids dissolved in the refluxing THF. The solutionwas allowed to cool down, and was transferred to another oven-dried,air-free 100 ml Schlenk flask provided with stir bar and rubber septumcontaining 5.0 grams of laboratory TOS slurried in 20 mL of THF. (Thetransfer of solution was performed inside the dry box.) The flask wasplaced in the oil bath and the mixture was stirred for about 30 minutesat 80° C., then flushed with a N₂ vent for about 4-5 hours until most ofthe THF evaporated. The resulting catalyst precursors further were driedfor 4 hours under vacuum (mechanical pump, 10⁻⁵ mmHg) in a water bath at45° C. The elemental composition of the laboratory prepared precursorswas determined by Induced Coupled Plasma (ICP) analysis and is reportedin the table below.

TABLE 7 Ti Mg Al (mmole/ (mmole/ (mmole/ THF Precursor gram) gram) gram)(weight %) Mg/Ti Precursor 1 0.268 0.841 0.466 13.4 3.1 Precursor 20.247 0.751 0.45 14.1 3.0 Precursor 3 0.303 0.814 0.498 13.0 2.7Precursor 1 comprised Davison 955 silica, had a magnesium/titanium ratioof 3, and is taken as a control. Precursor 2 comprised Ineos ES-757silica, and had a magnesium/titanium ratio of 3. Precursor 3 comprisedscreened Davison 955 silica, and had a magnesium/titanium ratio of 3.

When precursors having mole ratios Mg/Ti=5 were prepared, the MgCl₂loading was increased to meet this ratio (e.g., the ratio of Mg/Ti=5).To facilitate the solubility of MgCl₂ in THF, an amount of ethanol(ranging within EtOH/Mg mole ratios of from about 0.5 to about 2) wasadded to the THF solvent.

The light pink free-flowing powder precursors were then ready to betested in polyethylene polymerization reactions.

A one liter stirred stainless steel jacketed reactor-autoclave equippedwith a stirrer and a thermocouple was used for the polymerizationreactions with Precursors 1-3. The reactor was thoroughly dried under anitrogen purge at elevated temperatures (>100° C.) before each run.About 40 mL of dry, degassed 1-hexene (a co-monomer) was added viasyringe to the empty reactor that was cooled at 60° C. after purging,or, in certain experiments, 40 mL of condensed 1-butene was loaded toreactor by an automated injection pump. About 500 mL of dry degassedisobutane was converted into liquid in a pressure tower and fed to thereactor. At this point tri-ethyl aluminum alkyl (TEAL) was injected toreactor with a syringe as a dilute (1.54 M) heptane solution. The TEALacts as cocatalyst and also scavenges impurities (e.g., oxygen ormoisture) that could deactivate the catalyst. Unless otherwise noted,0.4 mmole TEAL was used in each experiment. The liquids were stirred at650 rpm while the reactor was heated until the working temperature of85° C. was reached. Next, a computer-controlled flow meter introducedabout 1000 or 1500 mL of hydrogen, after which (and by the samemechanism) ethylene was fed until the reactor reached a total pressureof 125 psi. The polymerization reaction then was initiated byintroducing 0.04 grams of laboratory catalyst precursor by means of apressure injection device, which further will be described. The finalpressure of the reactor was 380 psi. Ethylene was allowed to flow tomaintain its partial pressure of 125 psi. The reactor operativevariables (e.g., temperature, pressure and ethylene flow) were recordedalong the reaction time, and stored in a computer through a dataacquisition system. After a reaction period of 30 minutes, the ethyleneflow was stopped, and the reactor was depressurized to ambient pressurewhile the temperature of the reactor was reduced to about 45° C., atwhich point the reactor was opened. The mass of polymer produced by thereaction was determined after allowing all of the remaining comonomer toevaporate, until the polymer weight stabilized for a desired period oftime, which generally was in the range of from 1 to 4 hours.

The catalyst injection system used to conduct these experiments consistsof a 5 mL stainless steel cylinder provided with valves and connectorsin its extremes, coupled to a 50 mL cylinder that is attached via aflexible metal tubing to a 500 mL stainless steel bomb. The stainlesssteel bomb is capable of holding up to 400 psi of N₂. The catalystprecursor first was weighed and placed inside the 5 mL cylinder. About 5mL of isopentane was placed in the 50 mL cylinder. The cylinders thenwere coupled through the connectors, but valves (resembling globevalves) isolated the content of each from the other. All theseoperations were carried out inside a dry box. After loading thecatalyst, the device was removed from the dry box and connected to areactor port through the small cylinder. In a nearly vertical position,the 5 mL-50 mL cylinders tandem was connected through the extreme of thelarge cylinder to the bomb pressurized with N₂ at 400 psi by a flexiblemetal tubing. The bomb was isolated from the cylinders by another valve,such that the bomb could be pressurized either before or after beingconnected to the cylinders. Through a fast, and coordinated,opening/closing of valves, the nitrogen confined in the bomb pushed theisopentane contained in the large cylinder through the small cylinder,thus impelling the catalyst to the reactor. It was proved that thecatalyst was quantitatively transferred into the pressurized reactor.

The results of the polymerization tests using laboratory catalystprecursors are set forth in the table below.

TABLE 8 Activity Productivity Precursor Loaded Titanium Loaded Yield(grams PE)/ (grams PE)/ Run No. Precursor to Reactor (grains) to Reactor(mmol) (grams) [(mmol Ti)(h)] (grams Precursor) (comparative) 1Precursor 1 0.0768 0.02058 178 17,296 4,635 2 Precursor 1 0.0402 0.0107799 18,378 4,925 3 Precursor 1 0.0411 0.01101 99 17,976 4,818 4 Precursor1 0.0403 0.01080 101 18,703 5,012 Average: 18,088 Average: 4,847(inventive) 5 Precursor 2 0.0409 0.0101 152 30,092 7,433 6 Precursor 20.0404 0.0100 123 24,652 6,089 7 Precursor 2 0.0409 0.0101 191 37,8139,340 8 Precursor 2 0.0412 0.0102 135 26,532 6,553 9 Precursor 2 0.04080.0101 136 26,691 6,667 Average: 29,098 Average: 7,186 (comparative) 10Precursor 3 0.0408 0.01024 134 21,679 6,569 11 Precursor 3 0.0404 0.0122122 19,933 6,040 12 Precursor 3 0.0416 0.0126 131 20,786 6,298 Average:21,024 Average: 6,370

The laboratory-prepared catalyst precursors having amagnesium-to-titanium mole ratio of 3, with small particle size ES757silica (“Precursor 2”) demonstrated superior performance to thatdisplayed by other laboratory-prepared catalyst precursors havingsimilar compositions but different silica supports. These findings areadditionally supported, and may be better visualized, by FIG. 4, whichdepicts a plot of ethylene flow versus reaction time that was obtainedduring laboratory isobutane slurry polymerizations. FIG. 4 displays theethylene flow (as recorded by a computer-controlled Hastings mass flowmeter Model HFC 202) versus reaction time. The ethylene flow isexpressed as standard liters per minute (SLPM), which is the volumeoccupied by a given mass of gas at standard temperature and pressure(e.g., 0 degrees C. and 1 atmosphere of pressure). The representation ofthe ethylene flow during the reaction time may be referred to as the“kinetic profile.”

The greater ethylene uptake corresponding to laboratory preparedprecursors employing ES757 silica (as compared to precursors employingdifferent silica support materials) is consistent with the comparativelygreater yield of polymer product that was shown in Table 8.

A statistical analysis of the laboratory polymerization results(performed using software supplied by JMP Software) established thestandard deviation and confidence interval by analyzing the variance(anova). The analysis of the variance checks whether differences amongthe means exist.

The statistical results are presented in Table 9 The comparison betweenmeans and the corresponding 95% confidence interval indicates thatsilica Ineos ES 757 produced a catalysts precursor with activity that issignificantly higher than activity of catalysts precursors made withDavison 955 and Davison 955 screened (through 325 Mesh).

TABLE 9 Std. Std. Err. Lower Upper Level Number Mean Dev. Mean 95% 95%Davison 4 18,088.3 606.12 303.1 17,124 19,053 955 Screened 3 21,024.3826.22 477.0 18,972 23,077 Davison 955 Ineos 5 29,098.4 5,259.61 2,352.222,568 35,629 ES-757

Thus, Example 1 demonstrates, inter alia, that laboratory catalystprecursors prepared with silica support materials that have a smallerparticle size, a narrower particle size distribution and average porediameter of at least ≧220 angstroms may demonstrate desirableproductivity and may be useful in polymerization processes to generatepolymer products having desirable physical properties.

EXAMPLE 2

Scaled-up catalyst compositions were prepared in a pilot plantlaboratory using a jacketed vessel (that may be referred to as a mixtank) according to the procedure set forth below. The capacity of themix tank is on the order of about 2 pounds of catalyst material.

Silica dehydrated at 600° C. has a hydroxyl nominal concentration of 0.7mmole OH/gram. The TEAL-on-Silica (“TOS”) prepared for these scaled-upbatches has a target aluminum loading of 0.5 mmole/gram. As TEAL reactswith hydroxyl according to a 1-to-1 molar ratio, then about 0.2 mmoleOH/gram will remain unreacted on the TOS.

First, about 850 grams of silica were charged to the mix tank, for ES757silica and Davison 955-600 silica. About 3.5 liters of isopentane thenwere added, after which about 0.59 grams of 10% TEAL in isopentane (0.93ml) were added for every gram of silica charged. The TEAL reactsexothermically with the silica to form ethane. Accordingly, the TEALcharge was metered so as to keep the reactor temperature under a targetsetting of 35° C. The foregoing mixture was mixed for 30 minutes at apressure of 10 psig. Drying was initiated by heating the jacket to 60°C. and reducing the internal reactor pressure to 5 psig. A nitrogensweep was initiated. When the internal reactor temperature hadstabilized between 55° C. and 60° C. for 2 hours, the mix tank contentswere discharged. As noted above, the target aluminum loading for thescaled-up TEAL-on-Silica (scaled-up TOS) was 0.5 mmole/gram silica.

Scaled-up catalyst precursors were prepared according to the followingprocedure. About 3,500 grams of tetrahydrofuran (THF) was charged to themix tank. The water content of the THF was less than 40 ppm of water.Magnesium chloride (MgCl₂) was added to the dry THF. The mix tank waspressurized to 5 psig and heated until the contents reached atemperature of 60° C. Stirring at 150 rpm was initiated. About 38.6grams of ethanol were added, which dissolves the MgCl₂ almost instantly.Mixing continued for about 30 minutes, after which about 66.8 grams ofTiCl₃, 0.33 AlCl₃ were charged. The mixture was mixed for an hour. Themix tank then was cooled so that the temperature of the contents fellbelow 50° C. About 800 grams of scaled-up TOS was charged and mixed forabout 30 minutes.

The contents of the mix tank then were dried by heating the jacket ofthe mix tank to about 85° C., and reducing the internal pressure withinthe jacket by an incremental inch of pressure at a time until thepressure reached −5 inches of mercury. The internal pressure then wasreduced to full vacuum, and a nitrogen sweep was initiated. When thetemperature of the contents stabilized between 80 and 83° C. for threehours, the mix tank was pressurized to 5 psig, and cooled to below 40°C., at which point the scaled-up catalyst was discharged.

The catalyst precursors prepared as described above then were convertedinto catalyst compositions by treatment with at least one, and no morethan two, activators. The relative amounts of the activator(s) werevaried with respect to Ti content, to provide an Al:Ti molar ratio ofabout 1 to 5 of each one of the activators. First, about 800 grams ofcatalyst precursor was charged to a clean and inert mix tank. About1,600 grams of solvent was slurried into the mix tank. The mixture wasstirred at about 150 rpm, and the mix tank was pressurized to 5 psig.The mixture was mixed for 30 minutes, before drying was initiatedthrough heating the jacket of the mix tank to 60° C. A nitrogen sweepalso was begun, once the material became free-flowing. The material wasdried until the reactor temperature stabilized at about 57° C. for onehour. The mix tank then was cooled to below about 40° C., and thecatalyst composition contained therein was discharged therefrom.

Different catalyst formulations were prepared by varying the relativeamounts of the selected activators, one of them containing an halogenatom, in such a way that their respective Al/Ti molar ratios were withinthe range of from 1 to 5. A total of 9 different catalyst formulationswere prepared, comprising precursors prepared with both Davison 955 andES757 silicas. The catalyst formulations comprising precursors preparedwith Davison 955 silicas were labeled as A, C, D and E. The catalystformulations comprising precursors prepared with Ineos ES757 silicaswere labeled as A1, C1, D1, and E1. As each catalyst series progressesfrom A to E there is a consistent increase of the Al/Ti mole ratio forthe halogen-containing activator, which is accompanied by an increase,although to a lower magnitude, of the non-halogen containing activator.The sample catalyst compositions prepared as described above then wereused in polymerization reactions.

A one liter stirred stainless steel jacketed reactor-autoclave equippedwith a stirrer and a thermocouple was used for the polymerizationreactions. The reactor was thoroughly dried under a purge of nitrogen at100° C. for 1 hour and cooled down to 45° C. before each run. About 0.8mL of heptane dilute solution (1.54 M) of TEAL then was added to thereactor to act as cocatalyst and passivate any impurities. Afterstirring for 15 minutes, 0.15 gram catalyst was charged. The reactorthen was sealed, and 1500 or 3000 cubic centimeters of hydrogen wascharged as indicated in the tables that follow, after which the reactorwas heated to 65° C. At this point, ethylene flow was initiated, andcontinued until the reactor reached polymerization conditions of 200 psiat 85° C.

Ethylene was allowed to flow to maintain the reactor pressure at 200 psiduring the 30 minute reaction period. Ethylene uptake is measuredthrough a computer-controlled flow meter. The temperature of the reactorwas reduced to 45° C. while the reactor was depressured to ambientpressure, after which the reactor was opened. After allowing the solventto evaporate, the mass of polymer produced from the reaction wasdetermined. The polymer produced from the reaction then wascharacterized to determine a number of parameters, including Melt FlowIndex (MI), High Load Melt Flow (HLM), and bulk density (BD).

Tables 10 and 11 below set forth certain parameters determined fromlaboratory ethylene homo-polymerizations conducted as set forth abovewith experimental scaled-up improved precursors.

Table 12 sets forth certain parameters determined from laboratoryethylene homo-polymerizations conducted as set forth above withscaled-up catalyst formulations at activation Al/Ti ratios located inthe low end and in the medium end of the 1 to 5 range are compared toparameters of conventional Control Catalysts 1 and 4 (medium Al/Ti ratiorange, e.g., containing an Al/Ti ratio that is about 2.5) and ControlCatalysts 2 and 3 (at the lower end of the Al/Ti ratio range, e.g.,containing an Al/Ti ratio that is close to 1) at comparable Al/Tiratios.

TABLE 10 Activity H2 Loaded Catalyst Loaded Titanium Loaded Yield (gramsPE)/ Sample Catalyst to Reactor (mL) to Reactor (grams) to Reactor(mmol) (grams) [(mmol Ti)(h)] 13 Scaled-Up Davison 1,500 0.0490 0.012782 12,913 955 Silica Precursor 14 Scaled-Up Ineos 1,500 0.0408 0.0102111 21,764 ES-757 Silica Precursor

TABLE 11 Productivity Settled Bulk (grams PE)/ Melt Index (MI) Flow MeltIndex MFR Density Sample Catalyst [(grams cat)(hr)] (dg/minute) (HLMI)(dg/minute) (HLMI/MI) (grams/cm3) 13 Scaled-Up Davison 3,347 Not Not Not0.330 955 Silica Precursor Determined Determined Determined 14 Scaled-UpIneos 5,441 0.21 5.50 26.2 0.352 ES-757 Silica Precursor

TABLE 12 Productivity Settled Bulk H2 Loaded (grams PE)/ Melt Index (MI)Flow Melt Index MFR Density Sample Catalyst to Reactor (mL) [(gramscat)(hr)] (dg/minute) (HLMI) (dg/minute) (HLMI/MI) (grams/cm³) 15Control Catalyst 1 3,000 1,369 1.59 47.60 29.9 0.366 [Davison 955silica, Mg/Ti = 3] 16 Control Catalyst 4 3,000 760 1.00 29.60 29.8 0.390[Davison 955 silica, Mg/Ti = 3] 17 ScaleUp Catalyst C1 3,000 1,846 2.3875.20 31.6 0.342 [Davison 955 silica, Mg/Ti = 5, with ethanol] 18ScaleUp Catalyst E1 3,000 1,976 1.32 40.20 30.0 0.415 [Ineos ES-757silica, Mg/Ti = 5, with ethanol] 19 Control Catalyst 2 3,000 4,547 1.4041.20 29.4 0.272 [Davison 955 silica, Mg/Ti = 3] 20 Control Catalyst 33,000 2,655 1.50 45.90 30.5 0.323 [Davison 955 silica, Mg/Ti = 3] 21ScaleUp Catalyst A 3,000 3,698 1.20 35.80 29.8 0.285 [Davison 955silica, Mg/Ti = 3] 22 ScaleUp Catalyst A 3,000 5,141 1.40 42.50 30.40.336 [Ineos ES-757 silica, Mg/Ti = 5, with ethanol]

The relationship between productivity and bulk density of theexperimental scaled-up catalysts is illustrated in FIG. 5.

Example 2 demonstrates, inter alia, that the improved experimentalcatalysts prepared using supports that use ES757 silica having a smallerparticle size, a narrower particle size distribution, and a largeraverage pore diameter of at least ≧220 angstroms appear to demonstrate adesirable productivity-vs.-bulk-density relationship, which maycorrelate across a variety of magnesium-to-titanium ratios.

EXAMPLE 3

Sample catalyst compositions prepared in the manner described above werereacted in a polymerization process in a pilot plant reactor.

Polymerization was conducted in a 24 inch diameter gas-phase fluidizedbed reactor operating at approximately 300 psig total pressure. Thereactor bed weight was approximately 500-600 pounds. Fluidizing gas waspassed through the bed at a velocity of approximately 2.0 feet persecond. The fluidizing gas exiting the bed entered a resin-disengagingzone located at the upper portion of the reactor. The fluidizing gasthen entered a recycle loop and passed through a water-cooled heatexchanger and cycle gas compressor. The shell side water temperature wasadjusted to maintain the reaction temperature to the specified value.Ethylene, hydrogen, 1-hexene and nitrogen were fed to the cycle gas loopjust upstream of the compressor at quantities sufficient to maintain thedesired gas concentrations. Triethylaluminum cocatalyst was fed to thereactor in quantities sufficient to support reaction. Gas concentrationswere measured by an on-line vapor fraction analyzer. The catalyst wasfed to the reactor bed through a stainless steel injection tube at arate sufficient to maintain the desired polymer production rate.Nitrogen gas was used to disperse the catalyst into the reactor. Productwas withdrawn from the reactor in batch mode into a purging vesselbefore it was transferred into a product drum. Residual catalyst andcocatalyst in the resin were deactivated in the product drum with a wetnitrogen purge.

The properties of the sample catalyst compositions, and the results ofthe polymerization reactions are set forth in the tables below.

TABLE 13 Partial Residence Ethylene Productivity Time Pressure (lbs PE)/Productivity H₂/C₂ C₆/C₂ Sample Catalyst (hours) (psi) (lbs Catalyst)(Ti ICP-based) (mol/mol) (mol/mol) 23 Control Catalyst B 3.7 110 5,2573,709 0.155 0.142 [Davison 955 silica, Mg/Ti = 3] 24 ScaleUp Catalyst C4.8 110 6,160 6,552 0.142 0.113 [Davison 955 silica, Mg/Ti = 3] 25ScaleUp Catalyst C 4.0 79 6,114 4,383 0.147 0.137 [Davison 955 silica,Mg/Ti = 5, with ethanol] 26 ScaleUp Catalyst E 3.6 110 9,421 7,149 0.1230.110 [Davison 955 silica, Mg/Ti = 5, with ethanol] 27 ScaleUp CatalystD1 4.7 110 4,758 4,545 0.185 0.134 [Ineos ES-757 silica, Mg/Ti = 5, withethanol] 28 ScaleUp Catalyst D1 4.3 79 3,195 3,344 0.190 0.159 [IneosES-757 silica, Mg/Ti = 5, with ethanol] 29 ScaleUp Catalyst C1 5.0 1107,066 Not 0.166 Not [Ineos ES-757 silica, Determined Determined Mg/Ti =5, with ethanol] 30 ScaleUp Catalyst C1 5.5 79 5,085 4,985 0.138 0.149[Ineos ES-757 silica, Mg/Ti = 5, with ethanol] 31 ScaleUp Catalyst E13.7 110 9,005 4,202 0.146 0.126 [Ineos ES-757 silica, Mg/Ti = 5, withethanol] 32 ScaleUp Catalyst E1 5.0 79 4,780 8,419 0.136 0.146 [IneosES-757 silica, Mg/Ti = 5, with ethanol]

TABLE 14 C6/C2 Melt Index I₂ MFR Density Settled Bulk Sample Catalyst(mol/mol) (g)/[(dg)(min)] (I₂₁/I₁₂) (grams/cm³) Density (lbs/ft³) 23Control Catalyst B 0.142 0.945 32.54 0.9187 20.9 [Davison 955 silica,Mg/Ti = 3] 24 ScaleUp Catalyst C 0.113 0.707 31.26 0.9228 20.3 [Davison955 silica, Mg/Ti = 3] 25 ScaleUp Catalyst C 0.137 0.641 33.00 0.917620.5 [Davison 955 silica, Mg/Ti = 5, with ethanol] 26 ScaleUp Catalyst E0.110 0.627 34.04 0.9226 17.9 [Davison 955 silica, Mg/Ti = 5, withethanol] 27 ScaleUp Catalyst D1 0.134 0.759 30.38 0.9228 24.1 [IneosES-757 silica, Mg/Ti = 5, with ethanol] 28 ScaleUp Catalyst D1 0.1590.885 29.67 0.9178 23.7 [Ineos ES-757 silica, Mg/Ti = 5, with ethanol]29 ScaleUp Catalyst C1 Not 0.748 31.55 0.9180 21.9 [Ineos ES-757 silica,Determined Mg/Ti = 5, with ethanol] 30 ScaleUp Catalyst C1 0.149 0.90Not 0.9195 22.3 [Ineos ES-757 silica, Determined Mg/Ti = 5, withethanol] 31 ScaleUp Catalyst E1 0.126 0.727 31.42 0.9212 22.6 [IneosES-757 silica, Mg/Ti = 5, with ethanol] 32 ScaleUp Catalyst E1 0.1460.714 32.27 0.9176 22.1 [Ineos ES-757 silica, Mg/Ti = 5, with ethanol]

The above example demonstrates, inter alia, the inventive catalystsprepared with ES757 silica led to both enhanced productivity and polymerproducts that demonstrated, for example, improved settled bulk density.The unexpected increase of the resin bulk density with increasedproductivity is generally opposite to that demonstrated bypolymerizations conducted with conventional catalysts, and is highlybeneficial for the fluid bed gas phase operation. These findings arefurther illustrated in FIG. 6.

Therefore, the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned as well as thosethat are inherent therein. While the invention has been depicted,described, and is defined by reference to exemplary embodiments of theinvention, such a reference does not imply a limitation on theinvention, and no such limitation is to be inferred. The invention iscapable of considerable modification, alternation, and equivalents inform and function, as will occur to those ordinarily skilled in thepertinent arts and having the benefit of this disclosure. The depictedand described embodiments of the invention are exemplary only, and arenot exhaustive of the scope of the invention. Consequently, theinvention is intended to be limited only by the spirit and scope of theappended claims, giving full cognizance to equivalents in all respects.

1. A process for making polyolefins, the process comprising contacting,in a reactor, ethylene and at least one comonomer selected from thegroup consisting of C₃ to C₈ alpha olefin in the presence of a supportedcatalyst system, the supported catalyst system comprising at least onetitanium compound, at least one magnesium compound, at least oneelectron donor compound, at least one activator compound, and at leastone silica support material, the at least one silica support materialhaving a median particle size in the range of from 20 to 50 microns andan average pore diameter from 220 Angstroms to 265 Angstroms; whereinthe at least one silica support material has no more than 10% of theparticles having a size less than 10 microns and no more than 10% of theparticles having a size greater than 50 microns.
 2. The process of claim1, wherein the at least one magnesium compound has the formula MgX₂,wherein X is selected from the group consisting of Cl, Br, I or mixturesthereof.
 3. The process of claim 2, wherein the at least one magnesiumcompound is selected from the group consisting of: MgCl₂, MgBr₂ andMgI₂.
 4. The process of claim 1, wherein the at least one titaniumcompound has the formula Ti(OR)_(a)X_(b), wherein R is selected from thegroup consisting of: a C₁ to C₁₄ aliphatic hydrocarbon radical, a C₁ toC₁₄ aromatic hydrocarbon radical, and COR′ where R′ is a C₁ to C₁₄aliphatic or aromatic hydrocarbon radical; X is selected from the groupconsisting of Cl, Br, I and mixtures thereof; a is selected from thegroup consisting of 0, 1 and 2; b is 1 to 4 inclusive; and a+b=3 or 4.5. The process of claim 1, wherein the at least one titanium compound isselected from the group consisting of: TiCl₃, TiCl₄, Ti(OCH₃)Cl₃,Ti(OC₆H₅)Cl₃, Ti(OCOCH₃)Cl₃ and Ti(OCOC₆H₅)Cl₃.
 6. The process of claim1, wherein the at least one silica support material has a medianparticle size in the range of from 20 to 35 microns.
 7. The process ofclaim 1, wherein the at least one silica support material has a medianparticle size in the range of from 20 to 30 microns.
 8. The process ofclaim 1, wherein the at least one silica support material has a particlesize distribution in which no more than 10% of the particles have a sizebelow 12 microns, and no more than 8% of the particles have a size above50 microns.
 9. The process of claim 1, wherein the at least one silicasupport material has a surface area of at least 200 square meters pergram.
 10. The process of claim 1, wherein the at least one silicasupport material has an average pore volume of at least 1.4 ml/gram. 11.The process of claim 1, wherein the at least one silica support materialhas an average pore diameter of 225 Angstroms.
 12. The process of claim1, wherein the at least one silica support material has an average porediameter of 230 Angstroms.
 13. The process of claim 1, wherein the atleast one silica support material has an average pore diameter of 235Angstroms.